Mandrel for rolling-mills.



UH E

ROLLING MILLS.

ILnn MAYH, 1911.

MANDB APPLIOATI Patented Dee 19,1911.

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UNITED STATES PATENT OFFICE.

RICHARD mime, 0F BOUS-ON-THESAAR, GERMANY.

MANDREL FOR ROLLING-MILLS.

To all whom it may concern:

Be it known that I, RICHARD MtiHE, a subject of the Emperor of Germany, and residing at Bous-on-the-Saar, Germany, have invented certain new and useful Improvements in Mandrels for Rolling-Mills, of which the following is a specification.

My invention relates to mandrels for rolling mills, particularly for tube rolling mills, the object of my invention being to provide an improved mandrel which is more durable than those now commonly in use.

In the accompanying drawing a mandrel is shown in cross section in which my invention is diagrammatically represented.

As is well known, the mandrels employed in tube rolling mills are subjected to very heavy pressure during the rolling out of the tubes thereon. It has been found that according to the diameter of the mandrel different grades of steel must be employed, since mandrels of larger diameter behave differently under the heat of the rolling operation than do mandrels of smaller diameter. In the case of mandrels of small diameter a very hard steel must be employed, in order to prevent the too great and too rapid reductlon of its diameter by the tube forming rolls while heated during the rolling operations. In spite of all that can be done, the mandrels are so lengthened after a time that they must be brought back to the right length by jumping and to the right diameter by hammering in ooved molds. This reforging operation f or the mandrel is also forged to its original size and shape) has the effect of increasing the density of the exterior. surface of the mandrel to the depth of 2 or 3 millimeters, while the metal in the interior maintains its original density. This ap ears to be the reason for the appearance 0 cracks in the surface of the mandrel which soon occur during use, by reason of the cooling of the heated mandrel in water, since the denser outer surface obviously shrinks tighter, as it were, than the less dense mandrel core. This unequal shrinkage of the surface and interior of the mandrel, occurs also in hollow mandrels of the water or air cooled type. Experiments with mandrels of this type show that the same injurious surface cracks appear as in the solid mandrels, and this was clearly to be expected since the bore in these hollow mandrels can never exceed one-third the diameter of the mandrel by reason of the Specification of Letters Patent.

Application filed May 11, 1911.

Patented Dec. 19, 1911. Serial No. 626,529.

pressure which it must sustain in the forming rolls. The attempt to use hollow mandrels of this character was soon abandoned. So long as the surface cracks run lengthwise of the mandrel and do not become deep, its utility is not lost; usually however these cracks soon widen and the mandrel is thereby rendered useless. Of much more serious nature are cross cracks, which are very quickly followed by the breaking of the mandrel. The observation that these surface cracks increase in frequency the more often the mandrel is re-formed by jumping and reforging in the mold, led to the conclusion that, as above mentioned, the different density of the exterior and interior of the mandrel, (whether the latter be hollow or solid) promotes the formation of cracks, since every time the mandrel is hammered in the mold, the exterior shell of the man drel is rendered more dense and the occasion of the surface cracking increased. To counteract these disadvantages, resulting from the increased density of the exterior of the mandrel, it is now proposed to increase likewise the density of the interior of the mandrel. The present invention therefore, as shown by way of example in the cross section of the accompanying drawing, comprises a mandrel having not only its exterior surface a but also its interior surface I) of increased density. The particular form and diameter of the mandrel may of course be as desired.

Careful investigations have shown conclusively that the tendency to form surface cracks in mandrels having a denser exterior than interior, is markedly decreased if care is taken to increase also the density of the interior of the mandrel. This can of course only be accomplished in hollow mandrels. \Vhen the interior surface of the mandrel is also to be rendered more dense, this is readily accomplished simultaneously with the hammering of the exterior during the reforming of the mandrel. Any desired means may be employed to this end. A very simple method of accomplishing it is to insert a rod within the mandrel core and pass the mandrel with its contained rod, throu h a set of rolls in a rolling mill. But the m terior of the mandrel is rendered sufiiciently dense if the mandrel, passed over a solid core, is hammered in a mold. Investigations have also shown that hollow mandrels of this character, with interior and exterior surfaces of increased density, give a much longer service without cracking, and more than twice the usual number of tubes can be rolled thereon before the mandrel is rendered useless, and its eventual discard is usually the result of other defects than surface cracks resulting from its treatment in reforming.

Inasmuch as the consumption of mandrels in rolling mills is an item of great importance, the present invention of a hollow mandrel with both interior and exterior of increased density, is a matter of very great value to rolling mills. Aside from the additional life which mandrels of this character possess, the danger of breakage is greatly lessened, and this 1s of the utmost Importance since the breaking of a mandrel during the operation of the mill may result not only in the breaking of the rolls, couplings and the driving gear but even of the roll frame itself.

Naturally these improved mandrels may be employed not only in tube mills of the step by step type, but also in all tube rolling mills in which a mandrel is employed.

I claim as my invention A hollow mandrel having its exterior and interior-surfaces of greater density than the body of the mandrel.

In testimony whereof I have signed my name to this specification, in the presence of two subscribing witnesses.

RICHARD MUHE.

\Vitnesses:

M. BRUXMEIEB, IDA FISCHER.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner 0! Iatents. Washington, D. G. 

